Interrelationships between breeding frequency,timing and outcome in King Penguins Aptenodytes patagonicus: are King Penguins biennial breeders?

King Penguin Aptenodytes patagonicus chick growth is interrupted by a winter fast which extends the length of the breeding cycle (laying to chick independence) to 14–16 months, so that continuous annual successful breeding appears to be impossible. The 3–month laying period imposes further constraints with respect to timing of breeding attempts in relation to the onset of fasting. By the frequent resighting of individually marked birds at Marion Island, we examined the frequency of breeding and the relationships between timing, outcome and frequency in the same and in consecutive years. A total of 3101 adult King Penguins were banded between 1984 and 1991, yielding continuous breeding histories spanning a maximum of 5 years. Most penguins attempted to breed in consecutive years, although the likelihood of taking a year off increased with the number of consecutive attempts. In any one season, about 19% of potentially breeding adults did not breed. Early breeders were more likely to succeed than late breeders and comprised 84% of breeding attempts of known timing. Successful birds in one season usually bred late in the following season, whereas failed attempts were usually followed by an early attempt. Non-breeding was more likely to occur after a successful outcome than a failed one, and after a year off 93% of birds bred early. It is incorrect to refer to the King Penguin as a biennial breeder.     

Age-dependent prospecting and recruitment to a breeding colony of Short-tailed Shearwaters Puffinus tenuirostris

In a small colony of Short-tailed Shearwaters Puffinus tenuirostris , monitored annually since 1947, many of the young ringed as nestlings returned to their natal colony for one or more years before breeding for the first time. These 'prospectors' were first recorded at 4.1 ± 0.1 (range 2–7) years old; they started breeding at 7.0 ± 0.2 (4–14) years old. Overall, 31% of all prospectors bred on their natal island with no significant annual variation in this proportion. However, 8% of all natal recruits started breeding without having been recorded prospecting and bred first when significantly younger (5.6 ± 0.4 years old) than those first recorded prospecting. Shearwaters which subsequently bred at their natal colony started prospecting when significantly older (4.3 ± 0.1) than those that did not breed at their natal colony (4.0 ± 0.1 years). Non-natal recruits spent significantly less time prospecting (1.0 ± 0.1 years) than prospectors born on the island (1.9 ± 0.1 years). The shearwaters appeared to become progressively more faithful to the colony during their prospecting period.     

Measuring immigration and philopatry in seabirds; recruitment to Black-legged Kittiwake colonies

The degree of philopatry in two new Black-legged Kittiwake Rissa tridactyla colonies in northeast England was studied for 36 and 16 successive years, respectively. There was a tendency in both colonies for the number of recruits to the breeding group to increase with the age (and size) of the colony, but by an average of only one additional recruit each year. In the two new colonies, it was 7 and 9 years respectively before the first young birds bred in their natal colony. By that time, over 100 immigrants had recruited and bred in each colony. Thereafter, new philopatric birds were recorded annually. But these formed only an average of 23% of the recruits during 36 years (1955–90) at North Shields, and 4.2% over 16 years (1991–2006) at Coquet Island. In every year at both colonies the number of new immigrants exceeded the number of philopatric recruits. Males formed 82% of philopatric birds. The low degree of philopatry in the Kittiwake will result in appreciable gene flow between colonies and this is consistent with little geographic variation in the species. Each immigrant has to make a choice of which colony to enter, but the criteria for this selection are not understood. It is argued that many measures of philopatry in birds are biased towards high values because of the greater ease in identifying philopatric individuals. The generalization that there is a high degree of philopatry in colonial seabird species is not justified, as there is considerable variation between species, and possibly between colonies. More estimates based on unbiased data are needed.     

A population study of the Rook Corvus frugilegus in Leon Province, northwest Spain

A resident population of Kooks Corvus frugilegus in Leon, Spain, decreased by 247; from 197679. Migrant Rooks appear not to enter the range of this population which is unique in the Iberian Peninsula. During the breeding seasons colonies are attacked by man: 17–19% of birds failed to breed and only 0.5-0.7 young per nest survived to fly. The trees chosen for nesting are in plantations subject to regular cropping, after which colonies are scattered. Adult mortality was 16–26% annually. Young formed 17.6–23% of the population in June; 11–15.6% of birds in March were in their first year and many of these bred successfully. Communal roosts were used only from mid-July to mid-October.     

Population dynamics of the bearded vulture Gypaetus barbatus in southern Africa

The essential features of mortality and survivorship of bearded vultures Gypaetus barbatus in southern Africa were deduced from age class plumage characteristics. The population consisted of about 204 adult pairs within a breeding range of about 35,000 sq km. Pairs bred every year and produced, on average, about 0·9 young per pair per year. Young birds made up about 37% of the population, subadults 3·5% and adults 60%. About 182 fledged young were recruited to the population each year. The proportion of young birds in the population in different areas was inversely related to the breeding density of adult birds (range 24–47%). Young bird mortality over the four years to subadult age was 87%, the survival rate of adults was 94% and the mean lifespan of birds surviving to adulthood was 21·4 years. This study demonstrates the need to understand the relationship between adult breeding density and young bird numbers in different parts of their range to accurately deduce population dynamics characteristics.     

Age-related effects of a nonbreeding event and a winter wreck on the survival of Shags Phalacrocorax aristotelis

During 1993, about half the adult Shags Phalacrocorax aristotelis alive on the Isle of May, southeastern Scotland, failed to breed. The proportion not breeding was highest (66%) for individuals aged 14–21 years and lowest (12%) for those aged 3–6 years. In February 1994, a prolonged spell of onshore winds resulted in a wreck of these adults such that overwinter survival was reduced from the normal 88% to 14.7%. The age-specific pattern of survival over this winter differed from previous years, with birds aged less than 7 years and more than 16 years surviving less well and middle-aged individuals surviving better than expected. Whether an individual had bred or not in 1993 had little effect on the chances of survival of the youngest and oldest individuals, as most died. However, among Shags aged 12–15 years, those which had bred survived markedly less well than those which had not, indicating that there had been some cost involved to birds in breeding in 1993.     

Reproduction in an endemic bird of a semiarid island: a food-mediated process

We analyse the effects of rainfall, temperature, food availability and nest predation on the between-year variation in reproduction of the Canary Islands stonechat Saxicola dacotiae , a bird species endemic of the semiarid island of Fuerteventura (Canary Islands, Spain). We monitored the reproductive performance and output of the species across its whole distribution area during three consecutive breeding periods, also measuring rainfall, temperature and food (arthropod) availability on the ground monthly. Rainfall varied from 27.3 mm in 2000–2001 (dry year) to 124.5 mm and 125.1 mm (average years), respectively, in the 2001–2002 and 2002–2003 breeding seasons. The onset of breeding closely matched variation in the onset of the autumn-winter rains among years. Arthropod availability was strongly and positively related to rainfall one month before. Reproductive investment (number of clutches and clutch size) was correlated to arthropod availability both among years and among sites within years. Stonechat pairs bred once or did not breed at all in the dry year whereas they bred twice in the other two years. Clutch size was smaller in the dry year and larger in the second as compared with the first in the other two years. Reproductive investment largely determined reproductive output (number of fledglings) as there were no significant spatial or temporal variation in hatching success (90% on average) or nest predation (29% on average, mostly due to feral cats Felis catus ). Within- and among years variability in temperature or predation did not match variability in the onset, length or reproductive investment and output recorded throughout the study years. These results suggest that variability in annual fecundity in the Canary Islands Stonechat was mainly driven by rainfall through a food-mediated process.     

SEASONAL INCIDENCE OF BREEDING, MOULT AND LOCAL DISPERSAL OF RED-BILLED FIREFINCHES LAGONOSTICTA SENEGALA IN ZAMBIA

Red-billed Firefinches were netted and ringed in Lochinvar National Park, Zambia, in 1972 and 1973 and were netted sporadically through 1975. Most nested from March to May, i.e., in the late rainy season and in the early dry season, though some nested as late as August. Nearly all evidently bred in their first year. Moult generally began after breeding was completed, and the indicated average duration of moult was 3–5-4 months. The main foods taken at all times of year were seeds of the seasonal grasses Echinochloa colonum and Setaria spp.
Local population densities, estimated by two methods, were in the range 33–86 birds per km². Ringing results demonstrated overlapping activity ranges in the breeding season. Dispersal movements were non-directional, and varied up to 14 km. Some ringed birds moved regularly each year between a particular waterhole and a breeding site; other did not move from the site of original ringing. Most dispersal was evident in the dry season (June and July) and in the early rains (October and November). Genetically effective dispersal of young from the site of birth to the site of the first breeding season was up to 6'8 km, and some adults were netted in sites a few kilometres apart in successive breeding seasons. Some dispersing firefinches crossed the song dialect boundaries of the Village Indigobirds.     

The breeding biology of the Dalmatian Pelican Pelecanus crispus

The breeding biology of the Dalmatian Pelican Pelecanus crispus , a vulnerable bird species in the Palaearctic, has been studied for 7 years at Lake Mikri Prespa, a continental wetland and Tsoukalio lagoon, a coastal wetland within the Amvrakikos Gulf. The two colonies showed stability, with fluctuations in the number of breeding attempts each year varying by about 30% over a period of 7 years. The date of arrival at the breeding sites and the date of laying of the first egg varied between mid-February and mid-March. The egglaying period (including renesting) varied between 18 and 114 days between years. The annual average clutch size varied between 1.60 and 1.94 eggs per nest. The incubation period averaged 31.4 ± 1.4 days. The overall hatching success varied from 36% to 70%. Egg losses were mainly due to nest abandonment, infertile eggs and eggs rolled from the nests. The Dalmatian Pelican chicks took 11–12 weeks to fledge. Nestling mortality was very low in contrast to other species of pelican. Such a low nestling mortality explains why the breeding success each year is largely explained by the hatching success.     

The breeding biology of White-tailed Tropicbirds Phaethon lepturus at Cousin Island, Seychelles

During 1981–1983 the population of White-tailed Tropicbirds Phaethon lepturus at Cousin Island, Seychelles, bred aseasonally and asynchronously. The mean interval between consecutive successful breeding attempts was 273 days. Most individuals nested in the same site, and with the same partner, in successive attempts, but 7-5% of nest sites were used by more than one pair; 21 % of pairs which lost eggs, and 13% of those which lost chicks re-nested. Incubation lasted 40–41 days, with a mean incubation shift length of 6-6 days. Fledging periods varied between 67 and 89 days (mean 76-5 days). Mean fledging weight was not significantly greater than the average weight of breeding adults.
Fledging success was 36%. Many of the 39% of eggs which failed to hatch probably did so as a result of exposure to the sun's heat, following temporary desertion by adults which were themselves heat-stressed during incubation. Of the 41 % of chicks which died, most died young; many were probably killed by crabs Ocypode spp. Not more than 10% of all nest failures were due to nest site competition. A few chicks probably starved to death.
At the time of the study, both food and nesting sites were evidently in excess. A considerable increase in the size of the population will be possible before density-dependent control mechanisms begin to operate.     

Turnover and dispersal in a Peregrine Falco peregrinus population

In south Scotland, most Peregrines returned to the same territories to breed in successive years, though a few females changed territory from one year to the next.
Annual mortality among breeding birds was at most 9% among females (or 11% in both sexes combined). There may have been considerable annual variation, however, and excluding one exceptional year out of five reduced the estimate for females to 7%. These estimates are maxima, but are still considerably lower than those obtained from ring recoveries of dead birds reported by members of the public.
Among trapped birds, four males first bred at age two years, one at three and another at four or five; two females first bred at one year, 13 at two years old and one at three. Five other females which were seen to be in first-year plumage but were not trapped, also laid eggs, and 12 other such paired females held territory but did not lay. Only one paired male held territory in first-year plumage.
In their movements between natal and breeding territories, some females moved further than males, with median distances of 83 and 58 km respectively. In addition, of birds trapped breeding in the study area, a greater proportion of the males than of the females had been born locally, despite an equal sex ratio among fledglings; this was also consistent with a greater dispersal of females. In general, Peregrines made much longer movements in their first year of life than subsequently. Movements were in any direction.     

Breeding biology of the Barn Owl Tyto alba in central Mali

Data were obtained on 178 clutches of African Barn Owls in central Mali from four breeding seasons during 1979–1983. Significantly more clutches were laid in 1979–1980 and significantly fewer in 1980– 1981 than the average for the 4 years and there were significantly more clutches laid in the middle period of the annual breeding season. The egg volume was significantly smaller at the beginning of the breeding season and significantly larger in the middle than the overall mean with eggs of second clutches being larger than those of first clutches. The clutch size was 605 eggs of which 479 hatched. The number of young fledged per successful nest was 319 and was 1 83 for all nesting attempts. The month was the only variable shown to affect significantly the clutch size, eggs hatched and fledging rate, the highest success rates being associated with the middle of the breeding period. The average interval between the hatching of eggs was 2–31 days. Survival rates (47'1%) to fledging were significantly affected by year (1981–1982 being the least) and month (mid-season birds the best). The order of hatching significantly affected age at death or disappearance, the first-hatched birds surviving the longest. The year significantly affected age at fledging, the young from the year in which most clutches were laid leaving the nest at the youngest age and those associated with the year having the least number of clutches remaining in the nest the longest. The month of hatching also affected fledging age, birds at the extremes of the breeding season fledging at older ages. The discussion compares these data with those from elsewhere.     

Intermittent breeding in the short-tailed shearwater Puffinus tenuirostris

1.  At one colony of short-tailed shearwaters in Bass Strait, Australia, all birds breeding have been recorded individually each year for over 50 years. Among individuals known to be alive and to have bred before, 14% of each sex were not present at their breeding colony, on average, in any one year.
2.  A further 15% of males and 13% of females (a significant difference), known to have bred before, were present but not associated with an egg in any one year.
3.  Intermittent breeding was associated with pair bond breakdown and with a reduced ability to raise offspring, even when years of absence were allowed for.
4.  The frequency of attendance, laying and successful rearing of progeny to fledging increased with age in the early years of breeding. However, this was followed by a decrease, except in the case of laying frequency, which continued to increase throughout life.
5.  Our analysis indicated that intermittent breeding in short-tailed shearwaters did not result from individuals implementing trade-offs between the effort required for breeding success and their breeding life span. Rather, we suggest that individuals of higher quality are able to breed more frequently than others without any compensatory reduction in either their annual breeding success or their overall breeding life span.     

Effects of surgically implanted transmitters on swimming performance, food consumption and growth of wild Atlantic salmon parr

Experiments were conducted on wild Atlantic salmon Salmo salar parr to determine the effect of surgically implanted dummy transmitters on swimming performance, food consumption and growth. Swimming performance of tagged fish (tag 1·7–3·7% of fish mass) was similar to that of control fish 1, 5 and 10 days after surgery. Negative effects on growth, however, were found up to day 36 of a 45 day experiment (tag 0·9–2·6% of fish mass). Consumption rates were similar between tagged and control fish and did not explain differences in growth.     

The prevalence of non-breeders in raptor populations: evidence from rings, radio-tags and transect surveys

Age-specific survival and breeding (ASSAB) models were developed with data from 146 common buzzards ( Buteo buteo ) radio-tagged in southern Britain during 1990–1998, in a 120-km2 study area that had on average 25 egg-laying pairs. Survival checks were aided by philopatric behaviour and a maximum annual tag failure rate of 7%: minimum survival rates, that were estimated by assuming death of buzzards with lost tags, were close to maximum rates that were estimated using only the recorded deaths. First-year survival rate estimates for 35 buzzards fitted in 1990–1991 with 25–30-g backpack radios were 69–74% (minimum-maximum), close to the 61–71% for 16 buzzards with 12-g tail-mount radios; the backpacks transmitted for 2–4 yr. Overall survival rates were 66–73% in the first year, 91–97% in the second and 88–91% thereafter. Survival estimates from 288 recent British ring recoveries were lower in the first and second years, at 55% and 75%, but similar (88%) thereafter. Most deaths were from natural causes (40%) or interaction with artefacts (36%). ASSAB models, from radio-tracking and the observed 1.71 young clutch−1, predicted breeding by 16–21% of all the buzzards present in spring, or up to 25% with the minimum likely productivity of 1.4 young clutch−1 or 12% net emigration. Ringing data predicted breeding rates of 33–38%. The models were tested with density data from nest surveys and new radio-corrected-transect and truncation-mark-resighting estimates of buzzard numbers. Surveys in autumn and late winter estimated breeding rates of 21–25%. The high non-breeder density in spring, of three other buzzards for each paired bird with eggs, has important implications for understanding evolutionary fitness, predation and population ecology.     

Estimation and limitation of numbers of floaters in a Eurasian Sparrowhawk population

Over a 20‐year period, the numbers of Eurasian Sparrowhawk Accipiter nisus nests found in a 200 km² area in south Scotland remained relatively stable (mean 33.3 pairs, CV = 10.6%). Nest numbers fluctuated from year to year in a manner expected of a population subject to density‐dependent regulation. The numbers of non‐breeders (floaters) could not be counted directly, but the number of female floaters was estimated, using known mortality rates, from the numbers of females recruited to the breeding population each year at different ages. Female floater numbers were estimated by two methods: Method A assumed that birds bred for the first time in their first, second or third year, in the same ratio as they were found breeding for the first time in the study area; and Method B assumed that all third‐year birds found breeding for the first time in the study area had bred previously, unknown to us, outside the area. Under Method A, floaters consisted of some 1‐year and some 2‐year birds; while under Method B, floaters consisted only of some 1‐year birds. Under both methods, the estimated number of female floaters fluctuated greatly from year to year, but under Method A they averaged 0.90 per female breeder, and under Method B they averaged 0.28 per female breeder. The Method B estimate was most consistent with other data and with the finding that some birds found breeding in the study area were likely to have bred previously outside the area (because of territory changes). Moreover, the mean and variance in female floater numbers estimated by Method B were similar in magnitude to the values obtained in a simulation model. In this model, breeding density was given a fixed ceiling, while breeding success was allowed to vary from year to year within the limits observed in the study area. It was concluded that (a) recruitment of floaters to the breeding sector was density dependent with respect to breeder numbers, i.e. broadly speaking, floaters filled gaps in the territorial system left by the deaths and movements of established breeders; and (b) floater numbers themselves were probably not regulated in a density dependent manner, but depended on whatever was the balance between annual additions (from reproduction and immigration) and subtractions (from mortality, emigration and entry to the breeding sector).     

The influence of rainfall on diet and reproduction in four African rodent species

Arvicanthis nitoticus was found, during two seasons of the study, to begin breeding some two to three months after the start of the rains; at this time weed seeds first appeared in the stomach contents. Breeding continued during the rains and into the early part of the dry season while weed seeds and cereals formed the major part of the diet. Breeding declined during the early part of the dry season, and fat was laid down while weed seeds and cereals were still present but less abundant in the diet. Later in the dry season, breeding ceased and the diet was switched dramatically, first to the leaves and stems of dicotyledonous plants then almost exclusively to grass, and fat deposits were rapidly utilized. Arvicanthis living in an area where cereals were artifically supplied bred almost continuously. Mastomys natalensis also bred when seeds and cereals were most plentiful, but, by ranging widely over open ground, often managed to continue to find these foods, and insects, during the dry season. Supplied cereals failed to produce a reproductive response in Mastomys –instead, unprecedented fat deposits developed. Unseasonal reproduction in this species was, however, observed in an unseasonal wheat crop. Rhabdomys pumilio bred when cereals were plentiful but was also found breeding when its diet was mainly clover–a crop that is noted for its high crude protein content. The herbivorous Otomys angoniensis bred throughout the year and was unaffected by supplied cereals. It seems clear that the food supply of grani-vorous species is dependent on rainfall, and that prolongation of the normal rainy season may generate excess food and cover, resulting in and extended breeding season and unusually large numbers of these rodents.     

SEASONAL ABUNDANCE OF MUSCA VETUSTISSIMA WALKER AND OTHER CATTLE DUNG FAUNA IN CENTRAL AUSTRALIA

Abstract
Bush flies, Musca vetustissima attracted to a human, and arthropod fauna attracted to fresh cattle dung in 24 hours, were sampled every 2 weeks for 2 years (1980–1982) near Alice Springs in central Australia. Substantial rain fell in both summers, but it was more prolonged in the second. The bush fly occurred and bred throughout the year, although its abundance was usually low. The only major increase in bush fly abundance occurred after the first summer's rainfall caused the growth of new herbage. This was followed by increased feeding on dung by adult flies and intensified breeding. Bush fly abundance was low in the second summer, despite evidence of a long period of continuous breeding. A variety of dung-feeding and predatory beetles and also mites was almost always present, although numbers were usually low. The introduced dung beetles Euoniticellus intermedius and Onthophagus gazella numerically dominated samples. Dung fauna abundance also increased after significant rainfall, particularly in the second summer. Dissections of the dung beetles showed that they bred at these times.     

The adaptive value of energy storage and capital breeding in seasonal environments

Timing of reproduction in a seasonal cycle is a life history trait with important fitness consequences. Capital breeders produce offspring from stored resources and, by decoupling feeding and reproduction, may bend the constraints caused by seasonality in food or predation. Income breeders, on the other hand, produce offspring from concurrent food intake, with the disadvantage of less flexibility, but with high efficiency and no inventory costs of carrying stores. Here, we assess relative profitability of capital and income breeding in herbivorous zooplankton inhabiting seasonal, high-latitude environments. We apply a state-dependent life history model where reproductive values are used to optimise energy allocation and diapause strategies over the year. Three environmental scenarios were modelled: an early, an intermediate, and a late feeding season. We found that capital breeding was most important in the early season. Capital breeding ranged from 7–9% of the eggs produced but, because of the high reproductive value of early eggs, capital breeding ranged from 9–30% when measured in terms of reproductive value. The main benefit of capital breeding was reproduction prior to the feeding season – when the reproductive value of an egg peaked. In addition, capital breeding was also used to increase egg production rates at times of income breeding. For individuals born late in the season the model predicted a two-year cycle instead of the typical annual life cycle. These individuals could then reap the benefits of early reproduction and capital breeding in their second year instead of income breeding late in the first year. We emphasize the importance of evaluating reproductive strategies such as capital and income breeding from a complete life cycle perspective. In particular, knowing the seasonality in offspring fitness is essential to appreciate evolutionary and population-level consequences of capital breeding.     

Estimation of the number of brown trout Salmo trutta (L.) in Loch Leven, Kinross, Scotland

The numbers of adult trout in Loch Leven were estimated in April each year 1968–71 by tagging fish caught by seine net, and estimating the proportion of the total stock tagged from examination of the angling catch during June-August. The vulnerability of tagged fish before June and after August was higher than that of untagged fish. Tag losses, estimated by double marking, were 2.15 % over a whole angling season. The reporting rate of tag recaptures varied within and between years from 0.43 to 0.71. Differential mortality of tagged and untagged fish was unimportant, except in two subsidiary experiments when fish were tagged in June and August, when handling losses reached 2.7%. With adjustment for these measured errors, the stock of trout beginning their third or more years in the loch in April, fell from 126 665 in 1968 to 52 337 in 1971.